The present invention relates to a method of forming a lubricant layer on a magnetic disc, a device for forming the lubricant layer thereon, and a magnetic disc.
A magnetic disc is made by coating a magnetizable material on surfaces of a circular disc, which is made of aluminum, glass, etc., and it constitutes a part of a magnetic disk unit, which is a data recording device. The magnetic disc is attached to a rotary shaft and rotated at high speed. A magnetic head is held by a carriage mechanism and loaded on the surface of the magnetic disc. The magnetic disc is slightly floated by an air stream caused by the high speed rotation of the magnetic disc. In this state, the magnetic head is moved in the radial direction of the magnetic disc to read data recorded on the magnetic disc.
A basic structure of the magnetic disc is shown in FIG. 4. Magnetizable layers 54 are respectively formed on both surfaces of a disc 52; and carbon layers 56, whose thickness is about 10 nm, are respectively formed on the surfaces of the magnetizable layers 54 so as to protect the magnetizable layers 54 when the magnetic head contacts the magnetizable layers 54. Further, lubricant layers 58, whose thickness is less than 10 nm, are respectively formed on the surfaces of the carbon layers 56 so as to smoothly start and stop the magnetic head, which contacts the surface of the magnetic disc 50, and so as to protect the surfaces of the magnetic disc 50. In the present explanation, the disc 52, on which the carbon layers 56 are formed without the lubricant layers 58, is called the magnetic disc 50.
Conventionally, the lubricant layers 58 are formed by several methods. For example, as shown in FIG. 5, a solution 60, in which a lubricant is diluted with volatile solvent, is reservoired in a container 62, and a magnetic disc 50 is dipped into the solution 60. Then, the magnetic disc 50 is taken out from the solution 60 at fixed speed. By taking out at fixed speed, prescribed amount of the solution 60 can be stuck on surfaces of the magnetic discs 50. The solvent in the solution 60 stuck on the surfaces of the magnetic disc 50 volatilizes when the surfaces are exposed in the air, so only the lubricant is left on the surfaces, and the lubricant layers 58 can be formed on the magnetic disc 50. This method is called a dip-method.
Another method, in which the lubricant layers are formed as well as the dip-method, is shown in FIG. 6. The solution 60, which has been reservoired in a tank 64, is supplied into the container 62, in which the magnetic disc 50 has been accommodated, by a pump 66, and the solution 60 in the container 62 can be discharged and returned to the tank 64. While discharging the solution 60 from the container 62, the surface of the solution layer 60 is descended at fixed speed to gradually expose the magnetic disc 50. Then, the magnetic disc 50 is taken out, so that the lubricant layers 58 can be formed thereon. This method is called a surface descent-method.
In the methods, PFPE (per fluoro polyethers) is usually used as the lubricant; PFPE whose density is different from that of said lubricant, PFC, HFE and FC are usually used as the volatile solvent. Usually, one of them is selected as the volatile solvent.
However, in the conventional methods of forming the lubricant layers on the magnetic disc 50, the solvent volatilizes from not only the solution on the magnetic disc but also the solution in the container, so amount of the solvent in the solution is naturally reduced. To maintain the density of the lubricant in the solution, the solvent must be continuously added. But it is difficult to correctly know the present density of the lubricant because of continuously adding the solvent, so that the density of the lubricant cannot be precisely controlled and thickness of the lubricant layers of the magnetic discs must be dispersed. To maintain the thickness of the lubricant layers in a predetermined range, the thickness must be examined twice: after the steps of dipping and post baking. So the working efficiency must be low.